The product requirements for lipstick, which is one of stick-shaped solid cosmetics, are that it does not break or soften during storage, carrying, or use and that it can smoothly stick on the lips and impart a gloss.
However, in order to achieve shape-retaining ability that is necessary for lipstick, the hardness should be increased to a certain level. If the hardness is too high, the spreadability is poor during application and the gloss of an applied film is low.
Thus, it is difficult to simultaneously satisfy the requirements of the shape-retaining ability and a comfortable feeling in use, and this issue presents a big challenge.
Particularly, in recent years, lipstick that provides a smooth feeling in use is preferred. Therefore, soft lipstick is regularly produced, and it sometimes breaks during use especially in the hot summer, presenting a problem.
In order to prepare lipstick with smooth spreadability and high breakage strength, some attempts to blend various components have been made. For example, the blending technology of candelilla wax and hydrogenated jojoba ester is disclosed in patent literature 1. In patent literature 2, the blending technology of ethylene-propylene copolymer and a ditrimethylolpropane derivative containing a hydroxyl group is disclosed.
In patent literature 3, the container is designed so that lipstick will not easily break; in the disclosed technology, the lipstick supporting part is formed in a coil spring shape.
In patent literature 4, a stick-shaped cosmetic is disclosed in that a wax composition with high hardness is filled and solidified at the bottom of the inner holder, and the bottom portion of lipstick is connected with the wax composition at the top of the inner holder so that the lipstick is retained well by their mixing.                Patent literature 1: Japanese Unexamined Patent Publication No. 2004-224707        Patent literature 2: Japanese Unexamined Patent Publication No. 2004-339132        Patent literature 3: Japanese Unexamined Patent Publication No. 2002-191431        Patent literature 4: Japanese Unexamined Patent Publication No. 2005-168848        